The spots usually start as small dark green water-soaked areas. Within 48 hours, the lesions change to a brown color then to a gray or white and appear as sunken necrotic areas bordered by chlorotic tissue (on dark tobacco you usually do not see any yellow halo). The spots are often concentrated along the side of the midrib and large secondary veins but can be found anywhere on the leaf. On expanding leaves the spots appear near the tip. Lower leaf surfaces may show no evidence of damage in the early stages. Lesions may run together causing the leaf surface to become necrotic and fall out. Symptoms may occur at any growth stage, but most commonly occur during periods of rapid growth. Older leaves are more susceptible. Dark fired types usually show less injury than burley types when at the same growth stage and exposed to the same level of ozone.

Paul Bachi University of Kentucky Research and Education Center

The spots usually start as small dark green water-soaked areas. Within 48 hours, the lesions change to a brown color then to a gray or white and appear as sunken necrotic areas bordered by chlorotic tissue (on dark tobacco you usually do not see any yellow halo). The spots are often concentrated along the side of the midrib and large secondary veins but can be found anywhere on the leaf. On expanding leaves the spots appear near the tip. Lower leaf surfaces may show no evidence of damage in the early stages. Lesions may run together causing the leaf surface to become necrotic and fall out. Symptoms may occur at any growth stage, but most commonly occur during periods of rapid growth. Older leaves are more susceptible. Dark fired types usually show less injury than burley types when at the same growth stage and exposed to the same level of ozone.

Paul Bachi University of Kentucky Research and Education Center

The spots usually start as small dark green water-soaked areas. Within 48 hours, the lesions change to a brown color then to a gray or white and appear as sunken necrotic areas bordered by chlorotic tissue (on dark tobacco you usually do not see any yellow halo). The spots are often concentrated along the side of the midrib and large secondary veins but can be found anywhere on the leaf. On expanding leaves the spots appear near the tip. Lower leaf surfaces may show no evidence of damage in the early stages. Lesions may run together causing the leaf surface to become necrotic and fall out. Symptoms may occur at any growth stage, but most commonly occur during periods of rapid growth. Older leaves are more susceptible. Dark fired types usually show less injury than burley types when at the same growth stage and exposed to the same level of ozone.

Paul Bachi University of Kentucky Research and Education Center

The spots usually start as small dark green water-soaked areas. Within 48 hours, the lesions change to a brown color then to a gray or white and appear as sunken necrotic areas bordered by chlorotic tissue (on dark tobacco you usually do not see any yellow halo). The spots are often concentrated along the side of the midrib and large secondary veins but can be found anywhere on the leaf. On expanding leaves the spots appear near the tip. Lower leaf surfaces may show no evidence of damage in the early stages. Lesions may run together causing the leaf surface to become necrotic and fall out. Symptoms may occur at any growth stage, but most commonly occur during periods of rapid growth. Older leaves are more susceptible. Dark fired types usually show less injury than burley types when at the same growth stage and exposed to the same level of ozone.

Paul Bachi University of Kentucky Research and Education Center

Dark tobacco. Note "ring spot" on the leaves. This “ring spot” (also known as "star and crescent spot") which has the form of a necrotic spot encircled by alternating rings of healthy and injured tissue, with the necrotic rings being partial rings or broken lines, is described in an Agronomy Journal of 1971 as physiological in cause (not being caused by a pathogen, air pollutant, nutrient, or chemical). The book "Diseases of Tobacco" 3rd edition, puts this "ring spot" and the reference that says it is not caused by an air pollutant, under the category of weather flecking.We have sent similar samples in the past to a private laboratory for a tobacco virus screen and they have always come back with negative results.

Paul Bachi University of Kentucky Research and Education Center

Dark tobacco. Note "ring spot" on the leaves. This “ring spot” (also known as "star and crescent spot") which has the form of a necrotic spot encircled by alternating rings of healthy and injured tissue, with the necrotic rings being partial rings or broken lines, is described in an Agronomy Journal of 1971 as physiological in cause (not being caused by a pathogen, air pollutant, nutrient, or chemical). The book "Diseases of Tobacco" 3rd edition, puts this "ring spot" and the reference that says it is not caused by an air pollutant, under the category of weather flecking.We have sent similar samples in the past to a private laboratory for a tobacco virus screen and they have always come back with negative results.

Paul Bachi University of Kentucky Research and Education Center

Dark tobacco. Note "ring spot" on the leaves. This “ring spot” (also known as "star and crescent spot") which has the form of a necrotic spot encircled by alternating rings of healthy and injured tissue, with the necrotic rings being partial rings or broken lines, is described in an Agronomy Journal of 1971 as physiological in cause (not being caused by a pathogen, air pollutant, nutrient, or chemical). The book "Diseases of Tobacco" 3rd edition, puts this "ring spot" and the reference that says it is not caused by an air pollutant, under the category of weather flecking.We have sent similar samples in the past to a private laboratory for a tobacco virus screen and they have always come back with negative results.